1. Field of the Invention
The present invention relates in general to semiconductor lasers, and, in particular, to an improved laser diode driving circuit. Still more particularly, the present invention relates to an improved laser diode driving circuit for driving a variety of semiconductor lasers.
2. Description of the Related Art
Reduced scaling or shrinking of the geometries of devices used in integrated semiconductor circuit technology for forming denser circuits has required voltage supply sources to provide lower voltages than the heretofore generally accepted standard supply voltage of 5 volts so as to avoid a voltage breakdown in the smaller devices. These low-power circuits now typically operate in the 3.0 to 3.6 volt supply range.
The forward voltage drop of laser diodes has not decreased in proportion to the decrease in the supply voltage. Therefore, the number of circuits for biasing the laser diodes is limited. Further, it is desirable to develop a biasing circuit capable of being utilized with different types of laser diodes.
One known method for stabilizing the output of a semiconductor laser which fluctuates due to temperature changes includes a counter for controlling the laser power output in a feedback loop. The feedback loop includes a photodetector for detecting the current intensity of the laser beam emitted from a semiconductor laser. Its detected intensity is compared with a predetermined reference level. The count of the counter is updated so as to make the difference between the detected and reference values zero. The updated count is used to vary the level of the driver current to be supplied to the semiconductor laser. A
A need exists for an improved laser diode driver circuit capable of being utilized with various laser diodes in a low-power circuit.
An improved laser diode driving circuit is disclosed which includes a current source, an operational amplifier, a light sensing device, a current mirror, and a constant current source. The current source is coupled to the laser diode for biasing the laser diode. The operational amplifier has an output coupled to the current source for driving the current source. The operational amplifier includes a first and a second input. The first input is coupled to a reference voltage. The second input receives a feedback signal. The light sensing device is coupled to a first supply voltage for detecting a portion of an optical power output from the laser. The light sensing device generates a monitor current proportional to the detected optical power output. The current mirror is coupled to the light sensing device and the second input of the operational amplifier. The current mirror receives the monitor current and generates a mirror current which is substantially equal to the monitor current. The constant current source is coupled to the second input of the operational amplifier for outputting a reference current. The reference current and the mirror current are then utilized to generate the feedback signal.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.